Two novel carbon allotropes with tetragonal symmetry: First-principles calculations

Abstract

Two novel three-dimensional tetragonal symmetry carbon allotropes with space group P4/mmm are proposed based on density-functional theory in this work. The two carbon allotropes (denoted as tP24-II carbon and tP32 carbon) possess dynamic stability and mechanical stability, and tP24-II carbon and tP32 carbon are theoretically more favorable in energy compared to most other carbon allotropes. The Young's modulus E, shear modulus G and bulk modulus B of tP24-II carbon are greater than that of other P4/mmm phases (tP8, tP12, tP16, tP24 carbon, tP32 carbon), the E and G of tP32 carbon is the smallest among the P4/mmm phases in this work, while the B of tP32 carbon is greater than that of tP12 and tP24 carbon. For elastic anisotropy, the tP32 carbon has great elastic anisotropy in shear modulus and Young's modulus. Both tP24-II carbon and tP32 carbon are indirect band gap semiconductor materials, while the tP32 carbon is a wide band gap semiconductor material. Both tP24-II carbon and tP32 carbon may be potential materials for electronic devices.